UV inks have revolutionized graphics screen printing, but curing these finicky formulations remains a challenge to any shop interest in hig-quality, high-volume production. Besides matching ink characteristics with the correct curing parameters, printers must contend with power fluctuations that reduce dryer performance and high temperatures that can alter sensitive substrates and ruin registration on multicolor jobs. The printers at Joliet Pattern, Joilet, IL, know these problems well and decided to end them with a few modifications to their UV dryers. Joliet's production manager, Bron Wolff, describes how you can assess and improve your UV-dryer performance by learning from his company's experience.

I'd like to preface this article with a few simple statements that I believe to be fact. First, UV inks are not created equal. In fact, all colors within a given UV ink line will not cure the same under identical conditions. Second, light cures, not heat. Heat helps, but light--specifically UV light--is the key. Finally, more of anything is not necessarily better. This is especially true with UV curing, where more energy typically means more heat and more problems for the printer.

To be fair and honest, heat does play a part in curing. It improves the wetting properties of some UV inks, helps with crosslinking, and starts the post-curing process. But while a little heat can help the curing process, excessive heat can hinder it.

Initially, it wasn't heat that made us focus attention on our curing systems. It was unpredictable changes in curing-system performance. We found that jobs we cured successfully one week with particular lamp and belt-speed settings would fail to cure properly the next week, even though the settings remained unchanged and the curing unit was correctly maintained. As we eventually discovered, the problem didn't lie within our plant, but came from varying voltage levels supplied by our local utility company.

Powering UV-curing units

Power for manufacturing operations like ours comes from transformers located outside the plant. The power is rated in kilo volt-amps (KVA). A transformer rating of 25 KVA, for example, means that the transformer delivers 240 volts (triple phase) and 60 amperes per leg.